A lateral semiconductor device is formed, for example, using a silicon on insulator (SOI) substrate. As an example of a lateral semiconductor device, a lateral diode is known. At a surface portion of a semiconductor layer of the lateral diode, a cathode region and an anode region are formed. The anode region makes a circuit around the cathode region.
The lateral diode further includes a local oxidation of silicon (LOCOS) layer and a resistive field plate. The LOCOS layer is formed on a surface of the semiconductor layer and is disposed between the cathode region and the anode region. The resistive field plate is formed on a surface of the LOCOS layer. An end of the resistive field plate is electrically connected with the cathode region, and another end of the resistive field plate is electrically connected with the anode region. In the resistive field plate, a micro electric current flows. Accordingly, a potential distribution on the surface of the semiconductor layer between the cathode region and the anode region is equalized and a surface electric field of the semiconductor layer can relax.
As described in the patent document 1, when viewed in a plane, the resistive field plate includes a resistive field plate section having a spiral shape or a concentric circle shape between the cathode region and the anode region.